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Public doubts about the Three Gorges Dam’s role in flood control have resurfaced as communities along the Yantgze River, China’s longest waterway, battle the area’s worst floods since 1998.

The floods have wreaked havoc in the east, leaving 237 people dead and another 93 missing. That is on top of the 69 people killed when Typhoon Nepartak hit Fujian province on July 9.

More rain is forecast to hit the Yangtze River Basin this month, pushing flood defences to the ­limit 18 years after catastrophic floods in the vast catchment area took more than 4,000 lives.

Wuhan, midway along the Yangtze and home to about

11 million residents, has been particularly hard hit this year, prompting bitter questioning online about why major mainland cities had become increasingly vulnerable to extreme weather.

Many blamed poor urban planning and drainage while others put it down to land reclamation in wetlands to satisfy unbridled urban expansion over the past few decades.

Other critics raised doubts online about the Three Gorges Dam and its much-touted capacity to prevent floods. They circulated warnings by the late hydrologist Huang Wanli, who predicted that the dam would eventually fill with silt, and have to be demolished.

As censors rushed to remove the critiques from cyberspace, the authorities moved in to defend the world’s biggest hydropower project.

Zhang Jiatuan, a spokesman for the state office for flood control, said on Thursday that the dam “had played a quite big role in relieving flood control pressures”. Zhang said the dam reduced the amount of water flowing into Wuhan early this month when the city was drenched by record-breaking torrential rains.

[The dam] played a quite big role in relieving flood control pressures

Zhang Jiatuan, state flood control office spokesman

A Beijing-based association of science reporters also invited ­experts to laud the dam’s contribution in preventing water from surging towards downstream ­cities, Caixin reported.

Flood control has always been officially promoted as the Three Gorges Dam’s foremost priority. Hubei Vice-Governor Cao Guangjing was deputy general manager of the China Three Gorges Corporation in 2007 when he claimed the dam could prevent a catastrophic “one in 1,000-year flood”. The suggestion was the dam would prevent large swathes of the basin from such disasters.

That claim has since been ­watered down, with experts now saying the dam could withstand a once in a 1,000-year flood, and – together with other infrastructure – could protect the nearby cities of Jingzhou in Hubei and Chenglingji in Hunan from a once in a 100-year flood.

Tsinghua University engineering professor Zhou Jianjun said it was “dangerous” to rely on the dam for flood prevention, Shanghai-based news site Thepaper.cn reported. “The main task of the Three Gorges Dam is to protect the safety of the Jing River [a tributary of Yangtze in Hubei]. Most hydrologists have reached that conclusion, but many organisations and experts don’t want to talk about it openly,” Zhou said.

Zhu Fan, a Wuhan resident who endured the 1998 flood, said most residents knew that rainfall from surrounding regions – rather than the dam – had the biggest ­impact on the Yangtze’s water level in the city.

“I think many people now understand the main priority of the Three Gorges project is to ­generate electricity for business interests,” Zhu said. “But there is one problem with the dam that I think might lead to its eventual demolition, and that’s the sedimentation of sand and pebbles from the upper reaches.”

I think many people now understand the main priority of the Three Gorges project is to ­generate electricity for business interests

Wuhan resident Zhu Fan

Dam advocates dismiss such suggestions. In China Economic Review last week, Wang Yinan, a research fellow at the State Council’s Development Research ­Centre, said such criticism ­“demonised hydro construction”.

Nevertheless, sediment building up in the dam – and not being flushed into the lower reaches – means the clear, faster-flowing water from the dam is eroding ­riverbeds and banks, leading to riverbank collapses.

In April, Water Resources Minister Chen Lei told a flood control meeting in Wuhan that “the changes of water and sand conditions in the middle and lower reaches of the Yangtze over the past few years are intensifying the collapse of riverbanks”.

Zhang Boting, deputy secretary general of the China Hydropower Society, said the erosion by the clear water had lowered the Yangtze riverbed by 2.1 metres between Hubei and Hunan by washing away about 150 million cubic metres of sand.

The country has invested heavily in shoring up the river’s banks but the continued collapses could pose new flood safety risks on the Yangtze.

Chen promised more money for defences, with nearly 5 billion yuan (HK$5.8 billion) earmarked for Hubei alone until 2020 to ­prevent further collapses.

The funding could just be the start of the bottomless pit of investment that Huang predicted would be needed to address the problems caused by the dam.